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An A-Z Index of the Linux BASH command line
An A-Z Index of the Linux BASH command line
alias Create an alias
awk Find and Replace text within file(s)
break Exit from a loop
builtin Run a shell builtin
cal Display a calendar
case Conditionally perform a commandcat Display the contents of a file
cd Change Directorychgrp Change group ownershipchmod Change access permissionschown Change file owner and group
chroot Run a command with a different root directorycksum Print CRC checksum and byte counts
clear Clear terminal screen
cmp Compare two files
comm Compare two sorted files line by line
command Run a command - ignoring shell functions
continue Resume the next iteration of a loopcp Copy one or more files to another locationcron Daemon to execute scheduled commands
crontab Schedule a command to run at a later timecsplit Split a file into context-determined pieces
cut Divide a file into several parts
date Display or change the date & time
dc Desk Calculator
dd Data Dump - Convert and copy a file
declare Declare variables and give them attributesdf Display free disk spacediff Display the differences between two filesdiff3 Show differences among three filesdir Briefly list directory contents
dircolors Colour setup for `ls'dirname Convert a full pathname to just a path
dirs Display list of remembered directories
du Estimate file space usage
echo Display message on screen
ed A line-oriented text editor (edlin)
egrep Search file(s) for lines that match an extended expression
eject Eject CD-ROM
enable Enable and disable builtin shell commands
env Display, set, or remove environment variables
eval Evaluate several commands/arguments
exec Execute a command
exit Exit the shell
expand Convert tabs to spaces
export Set an environment variable
expr Evaluate expressions
factor Print prime factors
false Do nothing, unsuccessfully
fdformat Low-level format a floppy disk
fdisk Partition table manipulator for Linux
fgrep Search file(s) for lines that match a fixed string
find Search for files that meet a desired criteria
fmt Reformat paragraph text
fold Wrap text to fit a specified width.
for Expand words, and execute commandsformat Format disks or tapes
free Display memory usage
fsck Filesystem consistency check and repair.
function Define Function Macros
gawk Find and Replace text within file(s)
getopts Parse positional parameters
grep Search file(s) for lines that match a given pattern
groups Print group names a user is in
gzip Compress or decompress named file(s)
hash Remember the full pathname of a name argument
head Output the first part of file(s)history Command History
hostname Print or set system name
id Print user and group id's
if Conditionally perform a command
import Capture an X server screen and save the image to file
info Help info
install Copy files and set attributes
join Join lines on a common field
kill Stop a process from running
less Display output one screen at a time
let Perform arithmetic on shell variables
ln Make links between files
local Create variables
locate Find files
logname Print current login name
logout Exit a login shell
lpc Line printer control program
lpr Off line print
lprint Print a file
lprintd Abort a print job
lprintq List the print queue
lprm Remove jobs from the print queue
ls List information about file(s)
m4 Macro processor
man Help manual
mkdir Create new folder(s)
mkfifo Make FIFOs (named pipes)
mknod Make block or character special files
more Display output one screen at a time
mount Mount a file system
mtools Manipulate MS-DOS files
mv Move or rename files or directories
nice Set the priority of a command or job
nl Number lines and write files
nohup Run a command immune to hangups
passwd Modify a user password
paste Merge lines of files
pathchk Check file name portability
popd Restore the previous value of the current directory
pr Convert text files for printing
printcap Printer capability database
printenv Print environment variables
printf Format and print data
ps Process status
pushd Save and then change the current directory
pwd Print Working Directory
quota Display disk usage and limits
quotacheck Scan a file system for disk usage
quotactl Set disk quotas
ram ram disk device
rcp Copy files between two machines.
read read a line from standard input
readonly Mark variables/functions as readonly
remsync Synchronize remote files via email
return Exit a shell function
rm Remove files
rmdir Remove folder(s)
rpm Remote Package Manager
rsync Remote file copy (Synchronize file trees)
screen Terminal window manager
sdiff Merge two files interactively
sed Stream Editor
select Accept keyboard input
seq Print numeric sequences
set Manipulate shell variables and functions
shift Shift positional parameters
shopt Shell Options
shutdown Shutdown or restart linux
sleep Delay for a specified time
sort Sort text files
source Run commands from a file `.'
split Split a file into fixed-size pieces
su Substitute user identity
sum Print a checksum for a file
symlink Make a new name for a file
sync Synchronize data on disk with memory
tac Concatenate and write files in reverse
tail Output the last part of files
tar Tape ARchiver
tee Redirect output to multiple files
test Evaluate a conditional expression
time Measure Program Resource Use
times User and system times
touch Change file timestamps
top List processes running on the system
traceroute Trace Route to Host
trap Run a command when a signal is set(bourne)
tr Translate, squeeze, and/or delete characters
true Do nothing, successfully
tsort Topological sort
tty Print filename of terminal on stdin
type Describe a command
ulimit Limit user resources
umask Users file creation mask
umount Unmount a device
unalias Remove an alias
uname Print system information
unexpand Convert spaces to tabs
uniq Uniquify files
units Convert units from one scale to another
unset Remove variable or function names
unshar Unpack shell archive scripts
until Execute commands (until error)
useradd Create new user account
usermod Modify user account
users List users currently logged in
uuencode Encode a binary file uudecode Decode a file created by uuencode
v Verbosely list directory contents (`ls -l -b')
vdir Verbosely list directory contents (`ls -l -b')
watch Execute/display a program periodically
wc Print byte, word, and line counts
whereis Report all known instances of a command
which Locate a program file in the user's path.
while Execute commands
who Print all usernames currently logged in
whoami Print the current user id and name (`id -un')
xargs Execute utility, passing constructed argument list(s)
yes Print a string until interrupted
.period Run commands from a file
### Comment / Remark
An A-Z Index of the Linux BASH command line with examples
alias Create an alias
alias
Create an alias, aliases allow a string to be substituted for a word when it is used as the first word of a simple command.
SYNTAX
alias [-p] [name[=value] ...]
unalias [-a] [name ... ]
If arguments are supplied, an alias is defined for each name whose value is given.
If no value is given, `alias' will print the current value of the alias.
Without arguments or with the `-p' option, alias prints the list of aliases on the standard output in a form that allows them to be reused as input.
`unalias' will remove each name from the list of aliases. If `-a' is supplied, all aliases are removed.
`alias' and `unalias' are BASH built-ins.
The first word of each simple command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. The alias name and the replacement text may contain any valid shell input, including shell metacharacters, with the exception that the alias name may not contain `='.
The first word of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second time. This means that one may alias ls to "ls -F", for instance, and Bash does not try to recursively expand the replacement text.
If the last character of the alias value is a space or tab character, then the next command word following the alias is also checked for alias expansion.
There is no mechanism for using arguments in the replacement text, as in csh. If arguments are needed, a shell function should be used . Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt .
The rules concerning the definition and use of aliases are somewhat confusing. Bash always reads at least one complete line of input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias. This behavior is also an issue when functions are executed. Aliases are expanded when a function definition is read, not when the function is executed, because a function definition is itself a compound command. As a consequence, aliases defined in a function are not available until after that function is executed. To be safe, always put alias definitions on a separate line, and do not use alias in compound commands.
For almost every purpose, shell functions are preferred over aliases.
Examplesalias ls='ls -F'
Now issuing the command 'ls' will actually run 'ls -F'
Making an alias permanent:Use your favorite text editor to create a .bash_aliases file, and type the alias commands into the file. .bash_aliases will run at login (or you can just execute it with ..bash_aliases )
"The odds against there being a bomb on a plane are a million to one, and against two bombs a million times a million to one. Next time you fly, cut the odds and take a bomb." - Benny Hill Related commands:
export - Set an environment variableenv - Display, set, or remove environment variablesecho - Display message on screen readonly - Mark variables/functions as readonly shift - Shift positional parameters
Equivalent Windows NT commands:
HYPERLINK "http://www.ss64.com/nt/set.html" SET - Display, set, or remove Windows NT environment variablesSETX - Set environment variables permanently SETLOCAL - Begin localisation of environment changes in a batch file
awk Find and Replace text within file(s)
gawk (gnu awk)
Find and Replace text within file(s)
SYNTAX
awk 'PROGRAM'
awk 'PROGRAM' Input-File1 Input-File2 ...
If no Input-File is specified then `awk' applies the PROGRAM to
the "standard input", this can either be the piped output of some
other command or whatever you type on the terminal. Typed input will
continue until you indicate end-of-file by typing `Control-d'.
KEY
`-F FS'
`--field-separator FS'
Use FS for the input field separator (the value of the `FS'
predefined variable).
`-f PROGRAM-FILE'
`--file PROGRAM-FILE'
Read the `awk' program source from the file PROGRAM-FILE, instead
of from the first command line argument.
`-mf NNN'
`-mr NNN'
The `f' flag sets the maximum number of fields, and the `r' flag
sets the maximum record size. These options are ignored by
`gawk', since `gawk' has no predefined limits; they are only for
compatibility with the Bell Labs research version of Unix `awk'.
`-v VAR=VAL'
`--assign VAR=VAL'
Assign the variable VAR the value VAL before program execution
begins.
`-W traditional'
`-W compat'
`--traditional'
`--compat'
Use compatibility mode, in which `gawk' extensions are turned off.
`-W lint'
`--lint'
Give warnings about dubious or non-portable `awk' constructs.
`-W lint-old'
`--lint-old'
Warn about constructs that are not available in the original
Version 7 Unix version of `awk'.
`-W posix'
`--posix'
Use POSIX compatibility mode, in which `gawk' extensions are
turned off and additional restrictions apply.
`-W re-interval'
`--re-interval'
Allow interval expressions, in regexps.
`-W source=PROGRAM-TEXT'
`--source PROGRAM-TEXT'
Use PROGRAM-TEXT as `awk' program source code. This option allows
mixing command line source code with source code from files, and is
particularly useful for mixing command line programs with library
functions.
`--'
Signal the end of options. This is useful to allow further
arguments to the `awk' program itself to start with a `-'. This
is mainly for consistency with POSIX argument parsing conventions.
'PROGRAM'
a series of patterns and actions:
PROGRAM patterns and actions
The PROGRAM statement that tells `awk' what to do consists of a series of "rules". Each rule specifies one pattern to search for, and one action to perform when that pattern is found.
For ease of reading, each line in an `awk' program is normally a separate PROGRAM statement , like this:
PATTERN { ACTION }
PATTERN { ACTION }
...
However, `gawk' will ignore newlines after any of the following:
, { ? : || && do else
e.g. 2 patterns each followed by an action:
awk '/15/ { print $0 }
/40/ { print $0 }' BBS-list
A regular expression enclosed in slashes (`/') is an `awk' pattern that matches every input record whose text belongs to that set. e.g. the pattern /foo/ matches any input record containing the three characters `foo', *anywhere* in the record.
Comments - start with a `#', and continue to the end of the line:
# This program prints a nice friendly message.
`awk' patterns may be one of the following:
/REGULAR EXPRESSION/ - Match =
PATTERN && PATTERN - AND
PATTERN || PATTERN - OR
! PATTERN - NOT
PATTERN ? PATTERN : PATTERN - If, Then, Else
PATTERN1, PATTERN2 - Range Start - end
BEGIN - Perform action BEFORE input file is read
END - Perform action AFTER input file is read
In addition to simple pattern matching `awk' has a huge range of text and arithmetic Functions, Variables and Operators.
For full details see the info documentation
A few examples...
This program prints the length of the longest input line:
awk '{ if (length($0) > max) max = length($0) }
END { print max }' data
This program prints every line that has at least one field. This
is an easy way to delete blank lines from a file (or rather, to
create a new file similar to the old file but from which the blank
lines have been deleted)
awk 'NF > 0' data
This program prints seven random numbers from zero to 100,
inclusive.
awk 'BEGIN { for (i = 1; i